Mixed waste is a growing problem for today's technological society. The mixed waste generated by our Federal government and local electrical utilities sector is an increasing burden on these activities as well as a concern for the whole country in general.
The cost of disposing of mixed waste or transuranic/actinides in the U.S. are a multi-billion dollar per year program. The Department of Energy report Current and Planned Low-Level Waste Disposal Capacity Report Revision 1, Sep. 18, 1998 estimates the volume of low-level and mixed waste to be approximately 8.1 billion cubic feet during the period 1998 to 2070. All companies and institutions and businesses that generate and handle this category of waste or transuranic/actinides must provide safe, effective and preferably, inexpensive disposal of the waste or transuranic/actinides. In recent years there has been increasing concern over the disposal of mixed waste and/or transuranic/actinides. The principle method for the handling of this mixed waste and/or transuranic/actinides are self-storage or transportation to other facilities. The NRC and DOE have issued new regulations that require very stringent levels of control and maintenance of the storage facilities. The new regulations will, for practical purposes, require major modifications to almost all such storage facilities in the foreseeable future. Storage and transportation facilities have already begun to limit acceptance of mixed waste and/or transuranic/actinides, especially if it is from other then their own existing relationships Processes based on the use of silver, cobalt, cerium and peroxysulfate have been proposed, but each has severe limitations.
Research into the application of the MEO process to date has involved the use of the process to dispose of materials in several areas. In the first area, the MEO process uses an electrochemical cell in which the electrolyte is restricted to a composition of nitric acid and silver ions in a specific temperature, concentration, and pH range. The silver ions serve as the regenerable mediating oxidizing species which is used in an oxidative dissolution process to recover plutonium contained in solid waste from processes, technological and laboratory waste (U.S. Pat. No. 4,749,519), and subsequently extended to the dissolution of the plutonium dioxide component of uranium and plutonium oxide mixtures (i.e. mixed oxide reactor fuel) (U.S. Pat. No. 5,745,835).
In the second area, the MEO process was used for the oxidation (i.e., decomposition) of organic matter contaminated with radioactive materials, such as that contained in the solid waste generated in extracting plutonium from irradiated nuclear reactor fuel ( U.S. Pat. Nos. 4,874,485; 4,925,643.
Both of the two areas discussed have involved similar use of the MEO process using nitric acid and silver ions being generated by an electrochemical cell with the anode and cathode being separated by a membrane. The two uses have differed in the temperature range used in each of the applications. The first use is operated below 50° C. (i.e., generally around 25° C. or room temperature) to minimize water reactions with the Ag(II) ion, which are parasitic as they do not assist in dissolution of the plutonium dioxide, but do consume electrons, thus reducing the coulombic efficiency of the process. The second use is operated between 50° C. and slightly below 100° C. to promote reaction of the Ag(II) ions with the nitric acid solution which produces a range of highly reactive free radicals (e.g., .OH, .O2H, .NO3, etc) and H2O2, all of capable oxidizing organic materials.
Others have substituted cerium and nitric acid; and cobalt, and nitric acid, sulfuric acid or neutral solutions for the silver and nitric acid as the electrolyte (U.S. Pat. Nos. 4,686,019, 5,516,972, 5,756,874, 5,911,868, and 5,919,350). The temperatures vary among the electrolytes being substituted for the silver and nitric acid combination. Following the aforementioned work a U.S. Pat. No. 5,952,542, ruthenium (also mentioned are osmium, iridium, and rhodium) has been proposed as the electrolyte for the MEO process, to decompose organic materials in a slightly acidic solution operating between 60° C. and 90° C.
Most recently in U.S. Pat. No. 6,096,283, peroxydisulfate is used in a system combining hydrolysis and direct chemical oxidation (DCO). The hydrolysis is performed under the following conditions: at 100° C. ° C. to 120° C. ° C., a pH of greater than 7 and at greater than atmospheric pressure. The DCO is operated at temperatures at or less than 105° C. ° C., atmospheric pressure, and under alkaline, neutral and acidic conditions. The stated purpose of this patent is to destroy halogenated organic solvents, contaminated soils and sludge, and organic components of mixed waste.
All of the descriptions reviewed are similar in their application to the decomposition of organic materials and each patent has restricted the anions, cations, electrolyte, pH and temperature range used.
The processes defined in the foregoing patents each have severe limitations in their techniques and apparatus for using silver, cobalt, cerium and peroxysulfate. The silver based process requires the presence of strong nitric acid for the formation of a useful population of the Ag+2 oxidizing species and silver is removed from the system by parasitic reactions if halogens are present in the mixed waste. Silver ions diffusion across the membrane from the anolyte to the catholyte where it is necessary to conduct a recovery process due to the high cost of silver. Reduction of the concentrated nitric acid at the cathode ultimately leads to the formation of NOx in the cathode chamber, thus necessitating inclusion of a cathode off-gas treatment system.
The lower oxidation potential of cobalt and cerium species relative to many oxidizing species listed in Tables 1 and 2 herein, limit their ability to decompose some of the components of mixed waste and/or transuranic/actinides, at a practical rate. Both cobalt and cerium are costly for an industrial process and their migration through the membrane will require a recovery system.
This patent offer new features for an MEO process and apparatus not cover in the present art which address these limitations the features in this patent are: (a) alternative redox couple species, (b) different anolyte and catholyte electrolytes in the same MEO process and apparatus, (c) MEO apparatus design provides for the same apparatus using many different redox couples without changing the apparatus, (d) MEO process avoids the emission of NOx, (e) redox couples and electrolyte(s) can directly replace silver II in the existing apparatus to eliminate their major problems, (f) the redox couples dissolve plutonium oxides, nitrides or carbides, uranium oxides, nitrides or carbides, and other transuranics/actinides directly in to solution for ease of recovery.
These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the drawings.